Chromium plating baths which have been known include a chromium plating bath containing both trivalent chromium ions and hexavalent chromium ions. In order to make the most of the characteristics of the chromium plating bath containing both trivalent chromium ions and hexavalent chromium ions, the contents (content ratio) of trivalent chromium ions and hexavalent chromium ions in the bath have to be adjusted to predetermined values (a predetermined value). In general, such a plating bath is prepared by a method in which part of chromic acid is reduced to trivalent chromium ions by an organic acid. In the case of preparing the plating bath by this method, the contents (content ratio) of trivalent chromium ions and hexavalent chromium ions will vary depending on the degree of reduction of the hexavalent chromium ions to the trivalent chromium ions. Particularly, both the reaction of dissolution of chromic acid and the organic acid into water and the reduction reaction are exothermic reactions. Therefore, a rigorous temperature control is required for adjusting the contents (content ratio) of trivalent chromium ions and hexavalent chromium ions to predetermined values (a predetermined value).
Furthermore, the hexavalent chromium ion is highly hazardous and, hence, handling of the ion needs a sufficient control or management. Particularly, for avoiding leakage during transportation, it is desirable to obviate as securely as possible the transportation of the hexavalent chromium ions in the state of solution.
Besides, in the fields of utilizing plating films including a chromium plating film, there is a need for chromium plating films having more excellent characteristics, and there is also a need for simplified working steps from the viewpoint of reservation of natural resources and energy saving.
The following references relate to the present invention.
JP-B 46-40761
JP-A 52-125427
JP-A 59-185794
JP-A 59-223143
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